Science Buddies: "Ask an Expert"

Hi Irregular,

The carbon cloth is critical so try to find a source of this item. Here are some links that appear to offer this type of item:

http://www.jamestowndistributors.com/us ... rbon_cloth

http://www.uscomposites.com/

The first website mentions that carbon cloth is used in auto shops and for boats, so you might check a local auto or boat supply store.

The aquarium pump looks good; you just need a small pump to aerate the cathode chamber. You might try asking around to see if you know anyone who has an aquarium they are not using; you just need to borrow the pump for a few weeks.

Your other questions are excellent, and I will answer them tomorrow when I have a little more time.

Donna Hardy

Hi Donna!

Thank you very much for the carbon cloth links! I will look on ordering them tonight or tomorrow morning. We went to a few stores and asked about carbon cloth. I will mention it to my dad that we can check by calling an auto or boat store.

I have bought my small aquarium pump for the cathode. I will buy more if needed.

Here are my questions quoted so you don't have to go back and refer to them. I have edited them slightly:

irregular wrote: irregular wrote:
d. For my research paper, under History of Similar Experiments, what kind of experiments should I list/explain/describe? The Science Buddies for sure.. how many more? Maybe mention Bruce E. Logan and some experiments by children? How many experiments should I mention? In how much depth should I mention each experiment?
e. In your opinion, which variable will be appropriate for my experiment? I've narrowed it down to 3 - bacteria (topsoil+benthic bacteria), temperature or substrate? I am more hooked onto the bacteria and substrate options. The concerns of doing two variables is that 1) more time will be needed and it will be more complex 2)I will need to spend more money.



f. From my comprehension, in the cathode, I can make a hole to add the aquarium air pump as the electron acceptor. But won't this oxygen get into the salt bridge, into the anode? Then the oxygen won't be able to stay to serve as an electron acceptor.. and the anode will contain air...
g. Next, according to Bruce E Logan's article, the electrons and protons which meet in the cathode, combined with the oxygen produce water. But isn't a hydrogen molecule needed to combine with water molecule to produce a water molecule? If hydrogen is in the MFC, where does it come from? For a quantity of water to be produced, more than one molecule of water must be present! Glucose+oxygen produce water though.. in aerobic respiration..hmm..
h. In terms of wastewater as the source of bacteria, how does the water become usable and clean after the MFC process? Is the 'clean' water the generated water in the cathode? Because the wastewater in the anode will still contain bacteria...
i. I will be using a conductive solution in the cathode - saltwater, right? When the electrons and protons reach the cathode, what will the conductive solution do? After reading one reference, I thought that it was saying that the protons+electrons will oxidize the saltwater, then reduce the oxygen (kind of like the substrate and mediator?) which will produce water. Am I correct? The Bruce E. Logan MFC guide said that I just need to make saltwater, though the Science Buddies one said to buy distilled water and add salt to it. Can I just make saltwater?
j.Since reducing the internal resistance in the MFC is important, I did a little bit of research. I came to this paper which looks related to my project: http://www.springerlink.com/content/ep11306017977711/.

A concern of mine:
If you go to this link (http://www.microbialfuelcell.org/www/in ... jects.html) you can see in the pictures section that two students used chonical flasks (beakers) for the MFC. I used chonical flasks and a tube last year for my science project, so I have them left. It will be very convenient to use the chonical flasks since I won't have to use adhesives and tubing and soldering, etc. Extra chonical flasks+their tubes are readily available to me as well. My concern is that I cannot drill a hole in my chonical flask for the aquarium air pump since it will shatter. I would greatly appreciate if you have an idea of how I can still use the chonical flasks but not have the cathode electron acceptor (oxygen) problem. If nothing works, then I guess I will have to use containers/jars, etc.

Can I use graphite (pencil lead) as an electrode instead of the carbon cloth?

Lastly, will I need to purchase an agar plate or petri plate?

My dad told me that he will try to ask someone at work about carbon cloth, agar, the chonical flasks, etc.

Thank you very much for your time and patience, Donna!

Hi Irregular,

Thanks for putting all of your questions together. I have added my answers below after each of your questions.

d. For my research paper, under History of Similar Experiments, what kind of experiments should I list/explain/describe? The Science Buddies for sure.. how many more? Maybe mention Bruce E. Logan and some experiments by children? How many experiments should I mention? In how much depth should I mention each experiment?

Answer: For your research paper, you can refer to the papers or experiments you have found in the literature and just include the significant finding for the project, but omit the details. . For example, if you use the project that the science buddies website project was based on, you might state that a secondary wastewater sample was found to produce higher voltage in a microbial fuel cell compared to ground food wastewater.1

Then, your bibliography would have the corresponding reference.

1. http://www.usc.edu/CSSF/History/2008/Projects/J0804.pdf

For scientific papers like the following,

http://www.sciencedirect.com/science?_o ... b206d6d39b

the bibliography should be in the format specified by your teacher for this project. A standard format that I have used is:

Du, Zhuwei , et. al. Biotechnology Advances, 25 , 464-482 , 2007.


You should include a statement about all of the references you have found that are related to your project. You might have one paragraph of references on the significance of microbial fuel cells, the history of MFC’s, the construction of MFC’s, the function of bacteria in the microbial fuel cell, etc. If you have printed out all of your references, sort them into stacks according to topic and, after eliminating the irrelevant ones, make stacks according to topic, and then go through them one by one and write a one or two sentence summary of each. You will end up with an excellent background information section for your research paper.


e. In your opinion, which variable will be appropriate for my experiment? I've narrowed it down to 3 - bacteria (topsoil+benthic bacteria), temperature or substrate? I am more hooked onto the bacteria and substrate options. The concerns of doing two variables is that 1) more time will be needed and it will be more complex 2)I will need to spend more money.

A: I think you are on the right track to identify a suitable independent variable for your project. It will be difficult to control and temperature (although you should record the temperature during your experiments) and you already know from your background reading that anaerobic bacteria from benthic are the best for using in an MFC, so the idea of investigating the effect of a substrate is appealing. If I were doing this project, I think I would do one experiment with the freshly-collected benthic bacteria as a control and then try adding various substrates to the anodic chamber to see if the voltage in increase. In my local area, there is an oil refinery, a waste water plant that discharges into a bay, some superfund toxic sites, and several industrial plants that generate various types of industrial waste. I think I would try to get a sample from one of these sources and add it to the benthic bacteria to see if it could be used as a food source for the bacteria and generate electricity as the same time. If these samples were not available, then I would just use kitchen vegetable scraps (that would have been put into the garbage) ground up in a blender. (There is a growing movement to reduce the amount of garbage sent to landfills.) Any of these types of experiments would give your project a practical relevance.

f. From my comprehension, in the cathode, I can make a hole to add the aquarium air pump as the electron acceptor. But won't this oxygen get into the salt bridge, into the anode? Then the oxygen won't be able to stay to serve as an electron acceptor.. and the anode will contain air...

A: The salt bridge is made of agar, which is like jello, but doesn’t melt. The science buddies website has the best detail on how to make the salt bridges. All of the references we have seen have stated that the agar salt bridge effectively isolates the anode and cathode chambers. However, I noticed that many of the student projects have lots of wrapping materials around the salt bridge, so there must be a problem with leaking with some MFC’s.


g. Next, according to Bruce E Logan's article, the electrons and protons which meet in the cathode, combined with the oxygen produce water. But isn't a hydrogen molecule needed to combine with water molecule to produce a water molecule? If hydrogen is in the MFC, where does it come from? For a quantity of water to be produced, more than one molecule of water must be present! Glucose+oxygen produce water though.. in aerobic respiration.hmm..

A: The electrons from the anodic chamber travel through the wire connecting the two electrodes, the hydrogen ions travel through the salt bridge to the cathode chamber.

h. In terms of wastewater as the source of bacteria, how does the water become usable and clean after the MFC process? Is the 'clean' water the generated water in the cathode? Because the wastewater in the anode will still contain bacteria...

A: The water will still contain bacteria, but the water flowing through will have reduced BOD (biological oxygen demand) and COD (chemical oxygen demand) because the bacteria remove their nutrients from the water. Here is the Wikipedia website that explains how these parameters are related to wastewater quality. If these values are lowered, then the water quality is higher.

http://en.wikipedia.org/wiki/Wastewater

Here’s a reference that documents how a MFC can reduce BOD and COD:

http://www.microbialfuelcell.org/Public ... ngkong.pdf


i. I will be using a conductive solution in the cathode - saltwater, right?

A: Yes.

When the electrons and protons reach the cathode, what will the conductive solution do?

The electrons and protons will combine with the oxygen in the cathode chamber to produce water (H2O).

After reading one reference, I thought that it was saying that the protons+electrons will oxidize the saltwater, then reduce the oxygen (kind of like the substrate and mediator?)
which will produce water. Am I correct?

A: The saltwater in the cathode chamber reduces the resistance of the MFC, but the salt does not participate in the chemical reaction. When you get your multimeter, measure the resistance(ohms) of water and salt water to see the difference. The chemical reaction occurs at the cathode, where the hydrogen ions, electrons, and oxygen (from the aquarium pump bubbles) combine to form water.

The Bruce E. Logan MFC guide said that I just need to make saltwater, though the Science Buddies one said to buy distilled water and add salt to it. Can I just make saltwater?

A: I recommend using bottled purified drinking water as a starting point. This is the kind sold in gallon containers at the grocery store. Or, perhaps you have deionized water avai The science buddies website is slightly better because it has directions that start with water that contains no salt and tells you how much to add. This allows everyone who follows these directions to get the same result. There is a lot of variation in the composition of tap water and there could be chemicals that would affect the MFC. But the answer is if it is not easy to obtain distilled water, then yes, you could probably just use tap water and add salt. If the tap water in your local area contains lots of salt or other chemicals, then I recommend that you use bottled purified water from the grocery store to start with.

j.Since reducing the internal resistance in the MFC is important, I did a little bit of research. I came to this paper which looks related to my project: http://www.springerlink.com/content/ep11306017977711/.

A: You are getting to be very good at finding references. This article looks great, and I would be interesting in seeing the detailed results, but I don’t have access to it with my institution’s subscription. Are you close to a university where you could look up this reference, you would probably find that it is very relevant to your project because it includes an MFC design with low resistance.


A concern of mine:
If you go to this link (http://www.microbialfuelcell.org/www/in ... jects.html) you can see in the pictures section that two students used chonical flasks (beakers) for the MFC. I used chonical flasks and a tube last year for my science project, so I have them left. It will be very convenient to use the chonical flasks since I won't have to use adhesives and tubing and soldering, etc. Extra chonical flasks+their tubes are readily available to me as well. My concern is that I cannot drill a hole in my chonical flask for the aquarium air pump since it will shatter. I would greatly appreciate if you have an idea of how I can still use the chonical flasks but not have the cathode electron acceptor (oxygen) problem. If nothing works, then I guess I will have to use containers/jars, etc.

A: Do you have Erlenmeyer flasks? These are shown in the picture below, and would work perfectly for an MFC. It’s always better to use something that you have on hand. Please notice that the flasks are left open to ambient air.

http://www.microbialfuelcell.org/www/in ... jects.html


Lastly, will I need to purchase an agar plate or petri plate?

A: You will need agar, but not a Petri dish. Agar is melted by boiling it, then after it is cooled to about 55 degrees C, it is poured into the tube that will be the salt bridge. See the science buddies website for the details. You can get this at a health food store or Chinese grocery store. Ask your science teacher if there is any agarose available for you to use. You only need a few grams.

My dad told me that he will try to ask someone at work about carbon cloth, agar, the chonical flasks, etc.

A: Be sure and say thanks to your Dad. Did you tell your Dad that adding platinum to the cathode electrode will increase the voltage of an MFC? I don’t know how much money he wants to spend on your project, but you could tell him about this.


Donna Hardy

Hi Irregular,

I forgot to answer one question, about using graphite. As I recall, one of the Logan papers explained the choice of the carbon paper as a good choice because it has a high surface area compared to other electrode choices. Graphite that is used as in pencils has a small surface area, so would probably not work very well. I would keep looking for the carbon cloth.

I found a reference on MFC resistance that I can access and I will attach in this message and the next 3 messages. This recent paper is from Electrochimca Acta by Manohar and Mansfeld, two authors from USC. They used a sophisticated technique called electrochemical impedance spectroscopy to measure the resistance in an MFC . Their results are not relevant to your project, however, the paper is useful for your project because the introduction and experimental approach sections are particularly well done. You can use the basic format as a model for your paper, although, of course, the details of your project are completely different. Please note that the authors' experiment is very simple, they constructed an MFC and measured resistance with the anode chamber filled with stainless steel balls and did an identical experiment with the anode chamber filled with a test bacterium under anaerobic conditions. Also, of note, is that the authors used a cation exchange membrane to separate the anode and cathode chambers instead of an agar salt bridge, and they used carbon felt instead of carbon cloth. I also thought it was also interesting that the authors include a criticism of Logan's work in the first paragraph.

I hope you can complete the construction of your MFC in the near future. I have a feeling that you are going to need as much time as possible to complete the experiments. The science buddies website suggests monitoring the MFC for a month, but you will have to use a shorter time for your experiment.

Donna Hardy

Here's part 2.

Part 3.

Part 4 of 4.

RE: Questions f and g. To be clear about some of the finer points, you bubble air through the anode chamber to oxygenate the water there. The cathode chamber is supposed to be gas tight. The "salt bridge (electrical perspective) - agar gelatin (mechanical / biological perspective)" provides a means of electrons to flow through the salt crystal structure embedded in the agar gelatin and return through the PVC pipe connecting the two chambers. The manufacture of this salt bridge is supposed to create a liquid/gas tight seal between the two ends of the pvc pipe. If the salt bridge plug inside the pvc pipe leaks, then the apparatus will not operate in they way it was designed. Donna's observation about people having liquid leak issues where the pvc pipe mates with the plastic jars are probably situations where the pvc pipe fittings and the plastic jar material is a mechanical / plumbing / fit problem. The write up on how to accomplish the seal between the pvc pipe and the jar sounds like there are many possible failure modes depending on surface contaimination, differences in plastic materials, and how mechanically sound the glue joints end up in terms of torque, tension, vibration, they can withstand.

If I were attempting this, I might try a variation on the pvc fittings if I ran into leakage issues with the method described. For each end of each PCV pipe, I would try and come up with a 1/2 inch PVC electrical conduit male threaded adapter, two rubber washers whose ID (inside diameter) just fits over the 1/2 pvc threads, a stainless steel or brass washer whose ID fits over the 1/2 pvc threads, and an electrical conduit lock nut, and square plastic jar containers that have a flat side. By putting a rubber washer on the connector on both the inside and outside of the jar and using the steel/brass washer and conduit lock nut to make compress the rubber washers to make a liquid/gas tight seal with the plastic jar. My approach requires a tighten but don't over tighten too much so that the washers are permanently deformed and loose their elasticity.

Apparatus conustruction is something you may have to "experiment with" a bit if your first attempt has leaks or is not robust enough to transport.

Hi Craig and Donna!

DONNA:

In response to your questions, thank you so so so so so so so very much!!!! I really appreciate thisand it made things a lot clearer for me!

As for referencing, I am choosing to use the MLA format. So for parenthetical in text references the MLA format follows the procedure of shortening the webpage title. The expanded title and additional information on the link can be found in the references.

Thanks for the suggestions for my research paper!

For my variable, I chose to follow your advice. My first test will include using fertilizer/topsoil (organic compounds) as a substrate, and in the second MFC probably sugar as the substrate. Our city has a very significant engineering industry, so I may be able to purchase the waste water. If I cannot, I will think about using kitchen vegetable scraps as an alternative to the topsoil/fertilizer.

Hmm.. so a proton can is a hydrogen ion, right?

What will the conductive solution in the cathode do? Will the electrons+protons pass through it?

I will look over which type of water I can use for the conductive solution...

Unfortunately, I do not live near a university so I cannot view the article.

Yes, indeed I have Erlenmeyer flasks. I noticed the tube left open and was wondering how that student was successful in the experiment, with the oxygen seeping in..

I found the "All About Agar" page, and read up on that on the Science Buddies website. Thank you so much for telling me where to purchase agar - I called a health store and they carry it! They said that they have agar powder and agar plates, would I want the agar plates?

My dad contacted a chemical engineer who gave him a big catalogue of science materials. I looked in to see which I will need.. surprisingly, 25g of methyl blue was about $66! In my school board, there is a program called Adopt a Scientist. It was made up of retired scientists who volunteer to come to schools and do experiments with the students, and are also judges for the science fair I am participating in. We had one volunteer come in recently and she brought in methylene blue. I will try to see by my school if I can contact them and possibly borrow the methyl blue.

Thanks for the research paper and everything else!

CRAIG:

Thanks so much for having interest and helping me understand! It was very helpful indeed! Since I will be using two Erlenmeyer flasks + a tube as my MFC, I will not need to worry about PVC pipes, soldering, pipes, etc. The tube will be connecting both flasks, and it fits perfectly. For additional "just in case" reasons, I will wrap tape around the flask and tube fitting.

Thank you!

Hi irregular,

Looks like your project is going well. It sounds like you've done a lot of work so far. I just wanted to check in .

Hi Irregular,

It’s good that you have selected a standard format for the references.

I think your variables are good, but don’t forget to start with a control. For your project, I guess that would be an MFC with just the benthic mud sample to measure the baseline electricity. Your first independent variable would be adding the fertilizer/topsoil. A second experiment would be the sugar. A third variable would be the wastewater. Sounds like lots of experiments. That’s fine, but just do one at a time and see how it goes. How long are you going to test the sample? For a week? From what we’ve read, I think that would be a good time span.

Yes, a proton and a hydrogen ion are the same. The protons travel through the agar salt bridge and meet the electrons at the cathode electrode.

The conductive (high salt) solution in the cathode chamber allow the protons to travel through the cathode chamber. High salt solutions have lower resistance than plain water.

Can you get purified water in gallon jugs from the grocery store? Does your school have deionized water?

The cathode chamber needs oxygen; remember that the hydrogen ion and the electron need oxygen atoms to form water.

You actually want the dry agar. You will boil the agar to melt it, and then pour the cooled agar into the tubing to gel. The science buddies MFC website has the best directions for making the agar bridge. It will remind you of making jello, except agar melts at a much higher temperature.

Scientific supplies are expensive. It’s wonderful if you could get the methylene blue donated for your project. Be sure and acknowledge the donation on your project board if you do get it.

The Erlenmeyer flasks should simply the construction process, so I hope you can start the actual experiments soon.

Best regards,


Donna Hardy

Hi Donna!

Yes, the benthic mud sample, with just the organic compounds as my substrate (the mud I obtained the bacteria with) will be my controlled variable. I will be using the fertilizer/topsoil, sugar, and if possible the wastewater or kitchen vegetable scraps for my independent variables. That would be 3-4 MFCs. Since you recommend doing each MFC one at a time, though I have a time constraint, are you saying I should do one for one week, the next another week, and then possibly the last? If you recommend doing my experiment this way, I will then only have to do my experiment for each variable once.

Thanks for the clarifications Yes, I can get purified water in bigger quantities. My school does not have deionized water, unfortunately. I am looking to starting my experiment in the near future, once I obtain the methylene blue.

Thanks Donna!

Hi Irregular,

It sounds like you are about ready to start your experiments. The reason that I suggested doing one experiment at a time is that I thought you were going to make just one MFC. If you have the materials to make more than one, it would be better to run as many experiments as possible at the same time and you could run them for a longer period of time. That will give you more data. So, if you can set up 3 identical MFC’s at a time, you can run one control and two with independent variables; that would be excellent. However, if you can set up just one, that would work also. How many Erlenmeyer flasks do you have?

What is your plan to collect the benthic mud sample from the lake? Have you thought about how you will collect the mud? You will want to collect the mud in a bucket safely without falling into the water. And, since you are trying to collect obligate anaerobes, you will need to be careful about exposing the mud to the air. Your anaerobes could die if exposed to oxygen, or at least be inhibited for a while until conditions become anaerobic again.

What is the temperature of the lake? What is the current temperature of the location of your experiment?

Donna Hardy

Hi Donna!

Good news - I checked with my school and we had methylene blue! I also obtained some electrodes. The electrodes are thick, average sized rectangular shaped pieces. The problem is that the electrodes are made out of various materials such as aluminum, zinc, copper, etc. That means that there are no two electrodes which are alike. I just remembered that the electrodes are too big to fit into the Erlenmeyer flasks. Uh-Oh. I guess I will have to obtain the carbon cloth.

I could make more than one MFC if I can purchase/obtain more Erlenmeyer flasks, since I only have one set(2 flasks one big, one small, and a tube). I will talk to my dad about that tonight.

This is what the Science Buddies article says about the mud samples:

Making and Obtaining the Mud Samples

1. Go to the location of your stream where you have found the richest riverbed. The sample you get should not be full of rocks or twigs, just rich mud.
2. Tie the nylon rope securely around the middle of the PVC tube.
3. Throw the tube into the stream or creek. Make sure that you keep a good hold onto the end of the rope! Try to scoop as much of the stream bed as you can.
4. When you think that you have gotten a large enough sample, drag the tube back to shore. Gently tap the pipe with the hammer and transfer the sample into the bucket. Cover the bucket with plastic wrap and set it aside. Make sure to get enough of the benthic sample to fill the anode chamber and remember to use the sample within 24 hours.
5. Collect some of the stream water in the cleaned 1-gallon jug. Be careful when retrieving this sample. Always exercise caution when you are near a stream or a creek, as the water current can be stronger than it looks.
6. To make the second mud sample, use your trowel to place a few scoops of topsoil into the second bucket. Mix some tap water into the topsoil until you get a sludge-like mud. Cover the bucket with plastic wrap and set it aside.

I am planning on using this procedure, or maybe slightly varied depending on the choosing of the PVC pipe/bucket, etc. You are right about the anaerobes, they may die. However, the Science Buddies procedure doesn't mention that. I am assuming because, as you said, the bacteria just might be inhibited. What do you suggest for precaution that the bacteria don't die?

Since I am conducting my experiment in my furnace room, the temperature will be probably 5-10 degrees hotter than the house temperature.

My last concern is of the cathode. Since I will be using Erlenmeyer flasks, I will not be able to drill a hole through them. Since I cannot drill a hole, how will I attach the aquarium air pump tubing? If I drill a hole, the flask will shatter. What do you recommend?

Thanks Donna!

Hi Irregular,

Great questions!

Yes, you need the carbon cloth. The Erlenmeyer flasks are nice because they eliminate some construction and gluing, but you have to be able to get everything inside the flask, including the electrode. Have you tried an auto supply store? From the ads, it sounded like this item is used in auto repair.

If you have just two flasks, then make one MFC and try it out. If you make multiple MFC’s they would have to have identical containers for the anode and cathode chambers. We saw a picture of an MFC made with what looked like round flower vases. These are inexpensive. Do you have multiple identical containers that would hold about a liter in volume (1 quart)?

Your mud collecting procedure looks good. Have you checked out the lake to look for a site close to shore that has at least 2-3 feet of water with a mud bottom?

I just mentioned the problem with anaerobes so you would be careful and not mix air into the mud. Besides minimum mixing, I would recommend transporting the mud with some water covering it to protect it from oxygen. And you should collect the mud immediately before you set up the MFC.

The furnace room sounds good. In March, will the temperature be anywhere close to some of the optimum temperature we have seen in the literature? This would be about 25 degrees Centigrade.

You cannot drill holes in an Erlenmeyer flask. You will have to put the aquarium pump tubing and the electrode in from the top and drape the salt bridge from one flask to the next.

Donna Hardy

Hi Donna!

Okay, I realized that with the salt bridge, the aquarium tubing won't be able to fit. So my dad and I bought two inexpensive water bottles which look like these: http://www.greif.com/images/secondary-p ... handle.jpg, although smaller and thinner. The top has an opening, so that will be for the salt bridge. We bought a PVC tube for the salt bridge as well. I additionally bought the multimeter as well, it can measure in millivolts.

With this MFC, I will not need to obtain the carbon cloth I will be able to use the conductors, since the electrodes fit inside the bottle. The two conductors I am looking for usage is copper and copper zinc. I hope that they have similar conductivity level so my results as "equal", if you know what I mean. Last, since I will have to return the electrodes, how do you think I properly clean them to remove bacteria or mud, any impurities, etc etc.

The lake I am going to be accessing is relatively small and in a woodsy park. I have been to the park before but have not properly looked at the area. There is plenty of mud at the park, so I am assuming that there will be the needed mud. As for collecting the mud, I suppose that I could collect the mud with a bucket so I obtain water as well, for protection of bacteria.

One question for further clarification: the bottle I am using, obviously, will contain air and oxygen inside. When I place the mud inside, the bacteria will still be exposed to oxygen. Will I be putting water in the anode so the bacteria remains without contain of air?

Also, the Science Buddies project involves a mediator-less MFC. How much of the methyl blue do you recommend putting into the MFC?

I asked my dad about the temperature of the furnace room, and he told me about 25 degrees C! Why, won't that be perfect!

I am looking at buying the agar tomorrow, constructing the MFC tomorrow and possibly obtaining the mud and starting up tomorrow. If not possible, I will start up on Sunday. If everything runs smoothly, I will buy more of the identical bottles and pipe, and will create more MFCs.

Thanks so much for your patience, help, and checking up on me during my science fair process!

Hi Irregular,

Your bottles look perfect and your construction and start up plan sounds good too. The temperature in the furnace room is actually optimum, so that’s great. Do you have a thermometer so you can measure the ambient temperature in the furnace room during the experiments? It’s smart to start with just two bottles to plan to buy more after you verify this will work.

You will have to disturb the bacteria in the mud somewhat to collect them and to transfer to the anode chamber. I would try mixing in just enough lake water to make the mud a pourable slurry so you can transfer it to the bottle. It will be impossible to avoid introducing a little oxygen, but if you do the collecting and mixing the same way every time you set up the MFC, this should be a controlled parameter in your experiment. . Presumably, the mud will contain a mixture of facultative and obligate anaerobes, so if oxygen is introduced, the facultative (with or without oxygen) bacteria will be able to grow and use up the oxygen so the anaerobes can start growing again. This is an experiment, so if something unexpected comes up, you will have to make an executive decision and decide what to do. Scientists call this process trial and error.

There is a problem with your electrodes, however. If you use a copper and a copper/zinc electrode, you will be making a standard battery, and the current will be from a chemical reaction, and not only from the respiration of the bacteria. Here is an explanation:

http://www.miniscience.com/link/make_electricity.html

http://www.science.uwaterloo.ca/~cchieh ... ttery.html

With these two electrodes, the zinc will transfer its electrons to the copper. For your experiment, you want to measure only electrons from microbial respiration, so you should use two identical electrodes. I gather that you were not able to find the copper cloth, so you may have to wait until Monday to start and see if you can borrow a pair of identical electrodes (two copper or two copper/zinc). In an MFC, the electricity produced is dependent on the surface of the electrode, so you want your electrodes to be a large as possible. I don't recall any MFC's made with copper or zinc electrodes. Do you have time to check the references to see what has been used besides carbon?

You will be able to clean up the electrodes to return them without a problem. The mud should come off the metal electrodes with some soap and water.

If you do have two identical electrodes and can set this up today, try it first without the methylene blue.

If you do start your measurements today, measure both voltage and current.

Do you have a lab notebook to record your experiment as you go along? This will really help you remember exactly what you did at the end of the project when you are writing up the results.

I’ll check in tomorrow to see how you are doing!


Donna Hardy

Donna is correct, if you use a metalic electrode, it needs to be the same metal in both chambers.

Additionally, only use a single metal and not an alloy of more than one metal. The problem with alloys like Copper/Zinc is they can behave just like dissimilar metals in if they are in different solutions (one acidic and the other basic). One chamber might leach copper in to the solution and the other might leach zinc. Given that an MFC has and annode chamber and cathode chamber, the chemistry WILL BE DIFFERENT with respect to the oxidation/reduction of the electrode.

From a biologic perspective, your organisms might not like some metals. For example various copper compounds are used to control some organisms.

IMO: Flexible PVC tubing is NOT a good choice for a agar salt bridge. The salt bridge must:
1) be in contact with the solution in both chambers with no air gap
2) must not have a crack in it anywhere that blocks electron flow
3) must be large enough in diameter with respect to its length that its resistance is low enough for suffient electron flow to occur

The apparatus design in the science buddies project write up avoided some problems by:
1) using a rigid tube
2) attaching it between chambers below the top of the liquid level in both chambers
3) had a reasonable length to cross sectional area ratio
4) had the ability to have the resistance reduced by removing agar from either end

Hi Donna and Craig!

!) I do have a thermometer, although it is not located in our furnace room and we cannot remove it... I will see if there is any way I can measure it. I think that we have a clock at home which measures room temp, so I can possibly place that in the basement...

Thanks for clarifying the bacteria+oxygen concern!

2) Hmm.. thanks for bringing up the electrode problem. I wasn't so sure myself that it could work properly, but thanks to you and Craig, I know the right reason why. I looked back at my research papers and here were some electrodes that scientists used: carbon felt/cloth/paper/fibers/foam, graphite plates/rods, glassy carbon, graphite felt.

Current increases with overall internal surface area in the order carbon felt > carbon foam > graphite.

Thanks so much Craig for mentioning that bacteria might not like certain metals. I checked up on one of my papers and it mentioned that "metal anodes consisting of noncorrosive stainless steel mesh can be utilized, but copper is not useful due to the toxicity of even trace copper ions to bacteria. I think I will avoid using any of the metal electrodes I borrowed, and will contact stores to check for carbon cloth or carbon paper. What do you think about graphite?
EDIT: My dad and I thought of doing two things 1)combining many graphite pencil leads together or 2) purchasing carbon electrodes for welding from a local hardware store. Do you think purchasing carbon electrodes is a good idea?
EDIT: I was doing some research and stumbled upon this! http://www.instructables.com/id/Easy-Carbon-Electrode/ Do you think that making my electrodes this way is a good idea?

3) I got a little concerned when you, Craig, mentioned that PVC tubing is not a good choice. I then realized that I can use the tubing instead to obtain the bacteria from the lake, as the experimental procedure mentions. I think that the experimental procedure recommends using a PVC tube to collect the bacteria because of the minimality of bacteria in contact with oxygen.

Curious, I went to my materials and tried putting in the tubing once again, with the glass tube, in my Erlenmeyer flasks. I thought that I might have to use the flasks since the PVC tubing is not a good idea. My only problem with the PVC tubing was that it is flexible, and you recommended a solid salt bridge, since the tube had no air gap (it could fit inside of the water bottle's opening, so it is directly inside). Experimenting designs, I tried putting the glass flask rod into the opening of the water bottles. It fit!. That means that a part of the rod ends were inside the bottle. That means that there is no air gap, there is no crack, and the rod has a diameter of about 1.5 cm. The rod is U-shaped, though with a long bottom part and two short ends sticking up. The horizontal, main part is about 20cm, the length of the up-down part is about 8-9cm long.

4) I am concerned about:
a) Resistance of the glass. I found a relative link: http://www.springerlink.com/content/q6187r48ht1hh7n6/.
b) Reduced Resistance from agar.
c) Attaching the salt bridge below the top of the liquid. Since my salt bridge is at the top and the rod section inside the anode/cathode isn't very much, there is a problem. Could I fix it by making the MFC laying down, horizontal instead of vertical, kind of like the fourth picture on this page (http://www.engr.psu.edu/ce/enve/logan/b ... e_cell.htm)? However my design is obviously different because mine will have a salt bridge instead of a PEM, etc.

5)6Yes, I do have a lab notebook: they are indeed very handy. I will be measuring current and voltage, possibly resistance if you suggest. When you mean "without methylene blue", do you mean with no electron acceptor? How will the MFC work then?

)Lastly, I was reviewing my research paper and was not sure which information I should put when explaining bacteria. I don't think explaning the cellular composition of a bacterium will be needed, maybe just explain how a mediator can pass through a bacterium's membrane, etc. How about bacteria diets, classification, etc.?

Thanks so much!

Hi Irregular,

Thank-you Craig for your invaluable input!

Irregular, you are doing a great job of applying the background information to solving the technical problems involved with your project. You have identified a key factor for making a high-powered MFC. The reason that internal surface area increases the power output (carbon felt>carbon foam>graphite) is that more surface area allows more bacteria to contact the electrode surface to transfer electrons.

Here is a science fair project that compared 10 different materials in a microbial fuel cell, and found that Duocel Aluminum Foam Metal, 40
Pores Per Inch, 6-8 percent Density (Non-Compressed) gave the highest power to the microbial fuel cell.

http://www.usc.edu/CSSF/Current/Projects/J1004.pdf

The advantage of the DuoCell foam metal is that is has pores that are large enough for the bacteria to get in and attach; the MFC depends on bacteria transferring electrons to the electrode and, with a higher surface area, more electrons are transferred. The reason the science buddies website and most of the Logan papers use carbon cloth, is that is has a high surface area, it is non-toxic, and it’s durable.

The Wikipedia website on metal foams has pictures of foams. Can you see how the pores increase the surface area when used as an MFC electrode?

http://en.wikipedia.org/wiki/Metal_foam

Craig is right that copper inhibits the growth of many bacteria; it is used in aquarium tanks to inhibit the growth of algae and here is a reference that reports the problem of copper toxicity to bacteria:

http://www.sciencedirect.com/science?_o ... rticle.pdf

However, MFC’s have been successfully made using copper electrodes. Here are examples of two papers that used copper electrodes for this application. Unfortunately, I don’t have access to the details on the papers, only the abstracts.

http://www3.interscience.wiley.com/jour ... 1&SRETRY=0

http://cat.inist.fr/?aModele=afficheN&cpsidt=18928804

So, although the literature does indicate that a high surface area, non-toxic electrode material might be better, you should go ahead and use two identical copper electrodes if no other electrode material is available. But since there would be a performance advantage, you should continue looking for a source of the carbon cloth.

The carbon electrodes you are looking at look like they have less surface area compared to the copper electrodes, so there may not be any advantage to switching unless you can get carbon cloth or metal foam. If the carbon electrode has the same surface area as the copper electrodes, then there would be an advantage because it would be less toxic.

Now, the problem with the salt bridge. . . . The purpose of the salt bridge is to provide a path for the protons to travel to the cathode electrode. Since you are using two containers that are open at the top, the salt bridge will have to be a u-shaped tubular structure filled with agar with no gaps. We did see a picture of an MFC made with the u-shaped PVC, so this must be possible to do. Although from Craig’s comments, which are probably based on experience, it might be challenging to make one that contains agar with no gaps. I would recommend trying to make a salt bridge in a piece of u-shaped tubing that will connect the two containers you are going to use. Perhaps it would help to secure the u-shape with a piece of wire so it won’t move after the agar solidifies. If this doesn’t work, then the alternative is to drill holes in the sides of the bottles and make a straight salt bridge to connect the two MFC chambers. Or, maybe use a piece of filter paper as described in the Wikipedia website below. Or, use your imagination based on your knowledge of salt bridges. Here’s more helpful information on salt bridges.

http://www.warneronline.com/pdf/whitepa ... ridges.pdf

http://en.wikipedia.org/wiki/Salt_bridge

http://www.instructables.com/id/Simple- ... lt-bridge/

http://www.instructables.com/id/Simple- ... lt-bridge/

Is the glass rod you have a solid glass rod? If so, I don’t think it will work as a salt bridge. If it is a hollow tube, then you can fill it with agar according to directions; a non-flexible hollow tube made of glass would be easier to fill with agar, although as Craig mentions the surface area of the salt bridge is important; you want a surface area that is as large as possible. The elementary school battery project from yesterday’s post used a potato as a salt bridge. I wonder if a potato would work in an MFC?

I encourage you to keep going and set up the MFC with the materials you have, except not with two electrodes of different materials. You have lots of information and you should be able to solve any construction problems as you go along based on your knowledge of this subject. If something doesn’t work, you’ll have to try a different approach.

Yes, measure voltage, current, and resistance.

Donna Hardy

Hi Donna!

I understand the concept of more surface area and metal foam. The metal foam looks really amazing for MFC use, but my dad is not familiar with it and I am not sure if I will be able to obtain it. So basically I am looking for high surface area, low-toxicity and durability.

For my electrodes, I stumbled upon this link: http://www.instructables.com/id/Simple- ... lectrodes/

I have obtained the carbon paper (the article mentions it and so does one of my papers) and the aluminum wire mesh. I am currently wrapping the carbon paper on top of my rectangular zinc and aluminum conductors, and then wire mesh on top. I will be connecting the copper wire onto the wire mesh+carbon paper, not the conductor. The conductor is just to give the material shape.

Even though some people have used copper, I am doubting the material and want to use it as a last resort. As for the carbon electrode, I see from where you're coming from. If my current electrode doesn't work, my dad will obtain carbon electrodes from work which are a considerably good size.

I am eliminating the PVC pipe idea for the salt bridge. Instead, I will use it for mud collection. My glass tube(from the beakers) is U-shaped, and it is hollow, and non-flexible.

Hi Irregular,

The link you found is great! The carbon-paper-wrapped-in-wire-mesh construction will have a large surface area for the MFC electrode, and yet it sounds like it will be sturdy enough to hold up in the mud. This sounds like it is your best option for proceeding with your project, but it’s nice to have the back-up plan of using the carbon electrodes from your Dad’s work.

The hollow glass tube sounds like it will work nicely for the salt bridge. We have seen other references that use glass tubes for the salt bridge.

I don't think I have mentioned biofilms before, but these are described in several of the references we have read and are important for MFC's. A biofilm is a very dense population of microorganisms growing on a surface. Here is the Wikipedia website description of a biofilm:

http://en.wikipedia.org/wiki/Biofilm

I'm sure you are familiar with biofilms; this is the slimy surface that forms on surfaces that are under water. If you have a cat or dog water dish at home that has not been thoroughly scrubbed within the past 2 days, you can probably find a biofilm growing on the surface. Many bacteria and algae have the ability to form biofilms, or immobile layers of microorganisms stuck to the surface. Many times biofilms are not considered desirable because they are associated with dental plaque and shower mold, but in MFC's biofilms are associated with successful power generation. And if you think about it, it makes sense. If the bacteria are attached to the surface of the anode electrode, it will be easier for them to transfer the electrons to the electrode. It takes about 2-3 days for a biofilm to form on a surface, so after you set up your MFC, you should monitor the voltage, current, and resistance every 12-24 hours and notice if there is a difference at the time when you expect the biofilm to start forming.

Donna Hardy

Hi Donna!

Oh my, it seems wonderful to finally have my electrode and salt bridge concerns out of the way!Well, at least for now. Hopefully in my experiment everything runs smoothly. Okay, so far I have constructed the electrodes. As I said, I wrapped my Aluminum and Zinc electrodes in carbon paper, then wrapped aluminum mesh on top. I am wondering which will be the most effective way to keep the mesh attached to the carbon paper, and the carbon paper attached to the electrode. So far, I have used sturdy rubber bands. These rubber bands are 1.5 cm thick. Since bacteria on the rubber band will be ineffective as the band is blocking the mesh+carbon paper, I was thinking about other options. I was thinking about epoxy, but my dad noted that epoxy/glue might become ineffective as it will become in contact with water. What do you suggest?

From my reference:

Wire mesh layers should be placed on the outside to contain the carbon paper and maintain integrity of the electrodes in the mud or sand. The assembly should be tight to ensure good connectivity between the carbon and mesh layers plus circulation of media and water.

Apply solder liberally around the outside edge to ensure the best connectivity between the layers.

Once the electrodes have been assembled the exposed metal mesh should be protected with a good coating of hot glue.

A few questions:
1) Why is the mesh needed on top of the carbon paper? Is it because it will be more conductive?
2) Won't the carbon paper get wet or soggy?
3) What good properties does the aluminum mesh and carbon paper provide? Conductivity, toxicity, surface area, etc.
4) Do I need to attach the copper wire onto the carbon paper or the mesh?
5) In the MFC, the electrolyte will be agar, right?

Another question related to my research paper:

irregular wrote:I was reviewing my research paper and was not sure which information I should put when explaining bacteria. I don't think explaning the cellular composition of a bacterium will be needed, maybe just explain how a mediator can pass through a bacterium's membrane, etc. How about bacteria diets, classification, etc.?

As for biofilms, I saw the term in almost all my scientific papers, so yes, I am familiar with them. I can't stop noticing how very thoroughly and simply you defined a biofilm. I will monitor the voltage, current and resistance every 12-24 hours, as you recommend. If my data supports the fact that electricity was higher after 2-3 days, the mentioning of biofilms will be very useful in my conclusions and data analysis.

My dad will collect distilled water from his plant on Monday and bring it home, and we will collect the mud+start up on Tuesday.

Thanks a lot Donna!

Hi Irregular,

I don’t know how well the rubber bands will keep the carbon paper in contact with the aluminum mesh. How does it look to you? As you have noted, the directions for this electrode suggest using solder “liberally” around the outside edge and suggest completely coating the mesh with hot glue. Rubber bands oxidize quickly and break easily. You can check the conductivity of your electrode with the multimeter. If you check resistance between the carbon paper and the aluminum with your multimeter and if it’s infinite, then you need to do something else to ensure good contact between the aluminum and the carbon.

A few questions:
1) Why is the mesh needed on top of the carbon paper? Is it because it will be more conductive?

The aluminum mesh provides support for the carbon paper and provides a path for the electrons to flow to the copper wire connecting the anode chamber with the cathode.
2) Won't the carbon paper get wet or soggy?

Yes, it will get wet and soggy, but hopefully the aluminum mesh will hold it together well enough. Hopefully it will be durable enough to last through your project.

3) What good properties does the aluminum mesh and carbon paper provide?
Conductivity, toxicity, surface area, etc.

The function of the aluminum and the carbon is to provide a surface for the bacteria to grow on, and a place to deposit electrons.

4) Do I need to attach the copper wire onto the carbon paper or the mesh?

The aluminum should be in good contact with the carbon and you should connect the copper wire to the aluminum mesh.

5) In the MFC, the electrolyte will be agar, right?

In your MFC, the electrolyte is salt or NaCl. An electrolyte is small atom or molecule with a positive or negative charge. Sodium chloride, or NaCl, dissolves to make Na+ and Cl- ions. Here is the Wikipedia explanation of an electrolyte.

http://en.wikipedia.org/wiki/Electrolyte

The agar is a polysaccharide, like starch, made of individual sugar molecules and electrically, it is neutral and therefore has no charge. It is used to make a gel that forms the physical barrier between and anode and cathode chamber. You add salt to the agar when you make the salt bridge
http://en.wikipedia.org/wiki/Agar

I will answer the other questions later.

Donna Hardy

Hi Donna!

1)I checked resistance between the carbon paper and the aluminum, and it showed infinite with the multimeter (while the rubber bands were on). I do not have solder or hot glue at home. Do you think that it will be possible to apply non-toxic carpenter's glue?

Thanks for replying to my questions, and indicating that you will answer my last question later (relating to bacteria and my research paper).

2) Okay, so I have obtained all my materials, including distilled water.

Since the salt bridge needs to solidify all night, I have just come back from preparing it with my dad. We put a 100-125ml water+10g agar+2g fine sea salt solution into the tube and taped the tube onto a container to prevent spilling. The Science Buddies instruction included putting the tube in a petri dish - you said the petri dish wasn't required, and I didn't read about it in other procedures mentioning it either, so I skipped the relating step. I will check on the tube in the morning. If it has solidified, I will put it in a baggie and leave it in the fridge. In the evening, I will take it out to start my experiment.

3)The Science Buddies instruction is a mediator-less MFC. Since mine is a mediator MFC, how much of the methylene blue should I put into the anode?

So in the anode chamber I want the mud almost covering the entire electrode, and the methylene blue poured onto the mud, so it soaks in?

In my research report, last year, I organized the Background Research section by literally writing a heading each for question, variables, hypothesis, important terms/concepts (and listed and explained the various ones below), and questions relating to the subject. This year, I would like to make my report more professional. In what format should I do the Background Research section? One format is just providing an introduction, though I want to let the judges know everything I've learned. I will have a few paragraphs to explain the construction of an MFC, how it works, etc. Maybe after providing an overview of the working of an MFC, explain step by step in more detail, so I can emphasize concepts (e.g. oxidation)? If I do that, how do you suggest I organize my hypothesis, variables, question, objective/purpose, etc into my paper?

My main question in my experiment is concerning which substrate will produce most electricity in a MFC. To form my hypothesis, which resources to you recommend me reading and basing my hypothesis off of? I found:
http://pubs.acs.org/doi/abs/10.1021/es048927c
http://cat.inist.fr/?aModele=afficheN&cpsidt=16245394
http://www.microbialfuelcell.org/www/in ... trate.html

I know that acetate has produced one of the highest generation of electricity in MFCs, but I want to make sure that I know exactly why it produced the most, so I can add to my knowledge and know in case a judge asks me.

4)I am going to obtain the bacteria sample tomorrow afternoon. I will obtain a small quantity of lake water with the mud to make the sample a little "liquidy", as well. If I obtain a large quantity of mud and keep it in a properly secured bottle filled all the way to the top with mud, and not use it until about 6-7 days, will the bacteria die?

Thanks so much for all your time and efforts! I'm finally at the stage of my experiment!

With a methylene blue moderator, I am under the impression that the electrons will flow from the bacteria into the solute (water/methylene blue/and whatever other things are disolved) and then to the electrode.

With the moderator, I suspect you want to mix up the mud and solute to start with and then immerse most of the surface of the electrode into the solute leaving the connection to the wire above the solute level.

If you keep the connection point out of the liquid, it won't matter how you make the electrical connection to the electrode as long as it stays a good electrical connection that you validate with an ohm meter.

As far as how much methelene blue to use, you at least want the solution prior to mixing in the mud to show up as a light blue color. Your best source is to look at what others have done in terms of concentration.

Hi Craig!

Thanks so much for your explanation and helpful information!Yes, the methylene blue will take the electrons from the bacteria and then transfer them onto the electrode. Okay, I got your points. So I want to mix up the methylene blue+mud, and make sure the electrode is immersed in it, but copper wire on top, with no mud. My electrode is rectangular, so I will spread the wire on one side vertically, fold it underneath onto the other side, make sure it spreads vertically and let it continue out side the MFC. So basically its a U, with the electrode inside and one side of the U longer. And, last, the mud should become a light blue colour.

Wow, thanks so very much! My last reply to Donna is below and is updated, so please look at this new one, Donna.

Hi Donna!

1)I checked resistance between the carbon paper and the aluminum, and it showed infinite with the multimeter (while the rubber bands were on). I do not have solder or hot glue at home. Do you think that it will be possible to apply non-toxic carpenter's glue?

Thanks for replying to my questions, and indicating that you will answer my last question later (relating to bacteria and my research paper).

2) The salt bridge solution has solidified, not too solid though, it's like a solid gel. The 100-125ml water+10g agar+2g fine sea salt solution is now in the tube, in a baggie, and kept in the fridge until I start my experiment. The Science Buddies instruction included putting the tube in a petri dish - you said the petri dish wasn't required, and I didn't read about it in other procedures mentioning it either, so I skipped the relating step.

3)In my research report, last year, I organized the Background Research section by literally writing a heading each for question, variables, hypothesis, important terms/concepts (and listed and explained the various ones below), and questions relating to the subject. This year, I would like to make my report more professional and advanced. I want to emphasize everything I've learned. Maybe after providing an overview of the working of an MFC, explain step by step in more detail, so I can emphasize concepts (e.g. oxidation)... Here is my plan, and a few questions for you:

FINAL REPORT:
Abstract – (Is it needed?)
Introduction - (including what MFC is, how it works, purpose/objective, significance, relevance, question, hypothesis, experimenting manner)
Background Research - (a more in-depth explanation of “how it works” EXPLAINING rather than telling terms such as oxidation, along the way)
Materials and Methods
Data Analysis
Discussion
Results and Conclusions
Acknowledgments
Bibliography and References

DISPLAY BOARD:
Abstract
Question, Hypothesis, Purpose/Objective
Background Research
Data Analysis
Discussion
Results and Conclusions
Acknowledgments
Bibliography and References

*Where can I fit in MFC history, in my final report?*
*How can I explain the terms, while going through the process, without it getting overwhelmed, in the Background Research Section?*

4)My main question in my experiment is concerning which substrate will produce most electricity in a MFC. To form my hypothesis, which resources to you recommend me reading and basing my hypothesis off of? I found:
http://pubs.acs.org/doi/abs/10.1021/es048927c
http://cat.inist.fr/?aModele=afficheN&cpsidt=16245394
http://www.microbialfuelcell.org/www/in ... trate.html

I know that acetate has produced one of the highest generation of electricity in MFCs, but I want to make sure that I know exactly why it produced the most, so I can add to my knowledge and know in case a judge asks me.

I want to make sure that I know my stuff in-depth, very well. March Break is coming along so I will have additional time. I am thinking about studying which properties allow the methylene blue to enter the bacteria and grab the electrons. I'm inferring that the getting in part is easy. So then I think the mediator is conductive, so the electrons can conduct through, reducing the mediator...? Reduction means an add of electrons, right?

5)I went to obtain the bacteria sample this afternoon. I looked at three possible sources - 2 of which were frozen, one of which needed a long rope as the walkway was raised (a fishing area). The most rich place for the bacteria is probably one of the two which was frozen, as a nearby sign mentioned "soft mud". The ice was thin, so I was afraid of trying to break and step on it.

I will go to the soft mud area tomorrow with my dad with a shovel to see if we can break the ice. Even better, temperatures are supposed to rise towards the weekend. If it will break, great! If not, I will wait until the weekend and work on my paper more.

If I obtain a large quantity of mud and keep it in a properly secured bottle filled all the way to the top with mud, and not use it until about 6-7 days, will the bacteria die?

Thanks so much for all your time and efforts! I'm finally at the stage of my experiment!

Hi Irregular,

I'm glad you are working on your background paper along with trying to get your MFC set up.

Here are some answers:

1. Yes, I would try the carpenter’s glue; the electrode will not work at all with infinite resistance. This is a critical problem, and your MFC will not work until you have a usable electrode. Did you make two electrodes; one for the anode and one for the cathode chamber?

2. Don’t let the salt bridge dry out; the gel should stay well hydrated.

3. Your plan for a final report is a good one. The list of items for the introduction are all good, but you don’t have to include any details of the experiment in this section.

Yes, you do need an abstract with a complicated project like this. It will include a few sentences summarizing the project and will report what you found out. Everyone who sees your project will read the abstract; you teacher and the science fair judges will read all the details, but the abstract will help everyone understand what your project was about.

To explain all of the new terms, you might just include a brief explanation in the sentence with the new word. Or, you could consider just using the terms properly in the report and then include a glossary as an appendix so everyone reading the report will be able to understand it. The science fair judges will be interested in knowing if you understand your subject, so using the terms properly will be sufficient.

If you want to post your sections one at a time as you write them, I would be happy to help with comments.

The results on acetate as a carbon source have been reported in several references, including the 2 references here. The results have been reported empirically, and we haven’t seen an explanation. The higher power generated means that the bacteria in the MFC tested were able to get more energy from acetate compared to other carbon sources such as butyrate or glucose. Finding out exactly why, however, will have to wait until more detailed testing on the microorganisms found in MFC’s. Maybe you could answer this question in a future science fair project.

Just do one experiment and then do another if you have time. The methylene blue accepts the electrons from the bacteria and transfers them to the anode electrode. You could do an experiment without the methylene blue to see if it is needed for your MFC.

I know we have seen a reference with a recommended concentration of methylene blue, but I can’t find it. I’ll keep looking. But we have seen pictures of MFC’s with the methylene blue and Craig is right, the anode chambers look blue. If you do add the methylene blue, be sure and measure how much you add so you can set up every experiment the same way. The methylene blue should be one of your controlled parameters.

Collecting the mud sample from a frozen lake sounds like an adventure. The science buddies website suggests collecting the mud immediately before your use it, and this makes sense. With an MFC set up with freshly collected mud, the bacteria will be growing on carbon sources that are included with the sample. If you store the sample for several days in an enclosed container they will use up the available food and then stop growing (and stop producing power). So I recommend waiting to collect the mud until after your solve the problem with the infinite resistance on the electrodes.

I still owe you the explanation on bacteria for your background section.

Donna Hardy

Hello Donna!

1. Yes, I have made two electrodes for the anode and cathode, respectively. I will use the carpenter's glue right. now. So I will be putting the glue on the carbon paper, and gluing the aluminum mesh on top of the glue,... EDIT: Okay, it's almost an hour since I did that. This is extremely messy and I don't think that it will turn out good. My mom will proceed to buy a non-toxic epoxy tomorrow from the local dollar store.

2. To make sure that the salt bridge stays hydrated, I have kept it in a plastic baggie.

3. Okay, thanks for clarifying. The abstract shouldn't be a problem, since I wrote one last year. I was just making sure because many reports I'd seen online by students did not include an abstract. I guess they must've had an abstract in their display board.

As for the new terms, I think including a brief explanation with the new word might become overwhelming. The glossary idea is very intelligent, I will indeed use that idea. This will be great for being clear and showing what I know. Although if I do that, it will be pointless to explain how the MFC works in the introduction and in the background research (research paper) section. I will just include how it works in the research report section. Thanks very much for volunteering to comment on my sections, as I write them.

EDIT: As for the look of the paper and formatting, do you think it will be a good idea to keep the information in two-column, newspaper style, like we've seen in a few scientific papers? I am familiar on how to apply this technique into the document. Or, would you suggest normal text?

4. As a hypothesis, I could say that I think organic compounds as a substrate will be more effective than acetate because 1)the compounds may contain various nutrients/minerals/substrates 2)the bacteria live with the organic compounds as they depends on it as food, so they have grown used to it and survive well with it. OR, I could do some basic research on acetate and see if I can pull out something to do with electrons, salts, etc in acetate, and then further improve my hypothesis to support acetate. The "why?" is important in a hypothesis. My hypothesis wouldn't sound very strong if I said that I predict acetate will produce more electricity due to experiments, though the reason why isn't exactly discovered yet. If I showed evidence of some sort of personal research on acetate, I guess I could pull it off.

5. So I will be conducting two experiments, one with acetate, one with organic compounds. If I will have time, I will do more experiments. Since I cannot exactly "add" methylene blue in the anode after I test it without, I could use one paper I read to supply the information of why the methylene blue is needed. The paper I have read is called Electricity Generation by Microorganisms. The paper also mentions a drop or two shall do (of methylene blue). Okay, I will definitely measure the amound of methylene blue.

6. I have collected the bacteria today. Ah, you're right, what an adventure. The water wasn't that deep, it was near shore.. maybe 20cm deep? I collected water with it as well, to aid survival. We were about to start up the MFC right away, but had some guests over. So I will start the experiment tomorrow, right after my dad comes home from work. It will be less than 24 hours after we collected the sample. I will dispose the remaining mud and obtain fresh mud for my next experiment.

Thanks for remembering the bacteria issue.

You've helped me so much, I'm determined to make you proud. Thanks soooo much!

Hi Irregular,

1. I hope the epoxy works, good luck.

2. On the paper format, you can just use regular text. The two-column format is used when scientific papers are published, but there is no advantage. However, you can use whatever you think looks better to you.

4. Acetate is a small 2 carbon molecule and it has energy that bacteria can use. Maybe it works because it’s small and can get through the bacterial cell wall easily. Polysaccharides, found in organic waste, are much larger molecules, and have to be hydrolyzed to break them down to the individual sugars (5 of 6 carbons). This will take more enzymes and more energy for the bacteria. We have seen papers that report that butyric acid (a 4- carbon molecule) produces less power in an MFC compared to acetic acid. Maybe you will have time to do an experiment with a one carbon (formic acid) or 3-carbon (propionic acid). I don’t think we have seen papers that have tried these carbon sources, so this would make your project unique.

6. Your mud sounds perfect. If it was under 20 cm of water, it should contain lots anaerobic bacteria.
Let me know how your MFC works. I hope you can get it set up tonight.

Donna Hardy